I actually went through this last night.
I ride after work before heading home and had all my gear but...
I was tired
It was supposed to rain
My back hurt
My feet hurt
Blah, Blah, Blah
For me, I can sit around and think of a million reasons not to ride (or exercise) BUT, it only takes 1 reson to GO.
So you have to change your thinking a bit if you can. Instead of thinking about excuses, just try to think of 1 reason and it'll help.
Good luck!